Which problem with fasteners is most likely to cause joint failure?

• A. Over-torque
• B. Incorrect torque
• C. Worn threads
• D. Low lubrication

Answer: (B)

The key idea is that preload—the clamping force in the bolt—is set by the torque used when tightening. If torque is incorrect, the joint isn’t clamped with the right amount of force. Too little preload lets parts slip and vibrate, leading to fatigue, loosening, and eventual joint failure. Too much preload strains or yields the bolt and can strip threads, also causing failure. So, incorrect torque directly disrupts the necessary clamp load, making it the most common and impactful cause of joint failure. Worn threads, low lubrication, or other issues can worsen outcomes, but they typically affect or result from improper preload rather than being the primary cause.